Radio telephone system



May 9, 1939. D. A. HEISNER 2,157,234

RADIO TELEPHONE SYSTEM Original Filed Oct. 14, 1937 3 Sheets-Sheet 1 ATTO'CN Eye May 9, 1939. D. A. HEISNER RADIO TELEPHONE SYSTEM ori inal Filed Oct. 14, 1957 5 Sheets-Sheet 2 mwm 3 w AQWW r TM Hwwsmron:

DQHALD A. H'Enaflcn.

AT TORNEYS May 9, 1939. D. A. HEISNER RADIO TELEPHONE SYSTEM Original Filed 001.. 14, 1957 3 Sheets-Sheet 3 nun. 01

Patented May 9, 1939 aom'reo rs TATES PAT-EN T O F F lfCE RADIO TELEPHONE SYSTEM :Donald A..,Heisner, Lorain, Ohio, assignor to The Lorain Telephone .Company, Lorain, Ohio, .a

corporation of Ohio 10 Claims.

This invention relates tot-radio communication systems, and in particular to .-radio telephone circuits.

One object of this invention to-provide a system for controlling radio telephone receivers from a remote "location, .such a system being adapted for operation over ordinary wired lines, such as telephone lines or cables.

Another obj ect is to provide a radio telephone system having 'a receiving circuit in'twoportions, one portion of whichsislocated remotely from the othenportion and controlled by-means of wired communication devices.

oAnother object'is to-providea radio telephone receiving system having directional antennae, "andwa receiving circuitwdividedinto two parts, one part beinglocatecl in the vicinity'of the. antennae and the other ,part :being located remotely, with -means 'for controlling the operation of the firstpart fromthelocationaofthe second. part, particularly -as regards'the'selection of the desired directional antenna .andtheram plifying ,system associated therewith.

Another. objectis to provide a radio telephone receiving system having-a plurality ofdirectional antennae and an amplifier connected to each antenna ,atpne =location, connectedhy 'wired lines to-a .secondlocation, where means .is .pro- .vided for controllingthe selectiontand operation of the particular =-antenna and v,amplifienthe second .location .having circuits .for 1 completing the reception and .transformationof the=radio signal into..an audible signal.

Another object is to provide. aradio telephone receiving system, .as described above, wherein .meansis provided vfor automatically switching the audible .signal to alandtelephone line.

Another objectis to provide a radio telephone system having .a transmitter and. a receiver.in- .terconnected by a simplified relay switchingcir- .cuit in which a single relay performs the switching operations fromthe transmitter to the receiver, and viceversa, this relay being operated .in part .by received carriersignals and in part by voice currents being .transmitted.

Another object is to provide a radio receiving system having a lowpassaudio filter circuit ,connected. to.the loud speaker circuit during standby periods, and responsive to the reception .of a low frequency audio tone from thetransmitting station ,prior to each call, this being adapted to reduce the annoyance from static crashes during such stand-by periods whenthe receiving station isadjusted to high sensitivity While awaiting calls.

Another object is to provide a radio signalling system having a transmitter and a receiverinterconnectedthrough a switching system operatedby a single relay, which in turn, is controlled by a pair of electronic tubes, one tube being remitter by causing the voice currents and. car-.

=rier wave signal currents to operate switching means for'alternately switching in the receiver while switching out the transmitter, and vice versa.

Another object is to provide means for ad- .justi-ng the radio frequency detector circuit of a diode tuningcondenser to a condition permitting ganging of the diode tuning condenser with the amplifier grid and plate tuning condensers, thereby overcoming the difficulty hitherto'encountered of ganging these condensers, due to theqquite different load on the diode detector circuit than on the amplifier grid and plate cir cuits.

This-application is a division of my application, Serial No. 168,988, filed October 14, 1937.

Inthe drawings:

Figure 1 is, a circuit diagram showing a portion of. a radio telephone receiver located in the vicinity of a plurality of directional antennae. v

Figure 2 is a circuit diagram of another portion of the radio receiving circuit located re- .motely. from the circuit of Figure 1, and connected thereto by wired lines.

Figure 31s a circuit diagram of a radio receiver and transmitter interconnected by .an automatic switching arrangement, operated by .a single relay responsive in part to voice currents and in part to received carrier signals.

General arrangement In general, the radio telephone system of this invention consists of a transmitter and a .receiver, divided into at least two portions, one portion of the receiver being located in the vi cinity of the antennae and the other portion being located remotely and connected thereto by Wired. lineshaving controlling devices associated therewith. In particular, the receiverpreferably has two or more directional antennae,

with an amplifier associated with each antenna, both amplifiers being connected to an oscillator circuit employing a fixed oscillator frequency. The selection of the particular antenna and amplifier is made through wired lines running from the receiver control station.

The receiver shown uses the superheterodyne circuit with a single frequency or a narrow band of frequencies, the intermediate amplifier being capable of being tuned. This tuned amplifier is located at the receiver control station, which is at a considerable distance from the receiving antennae and associated amplifiers. The signals amplified by the intermediate amplifier at the controlling station are, in turn, amplified by an audio amplifier and conducted either to a loud speaker or head phones, as desired. A transmitter is located at the receiver control station and selectively connected to a land telephone line by a relay-operated switching arrangement, the relay being operated in one direction by the plate current received from a tube responsive to receiving carrier signals, and operated in the opposite direction by a tube responsive to transmitting voice currents. The former tube operates the relay to place the receiver in connection with the land telephone line, and the latter tube operates the relay to place the transmitter in connection with the land telephone line.

Associated with the loud speaker circuit is a low pass filter system, which permits the passage of a low frequency calling tone from the distant station, but filters out the higher frequency tones resulting from static. In this manner the static annoyance during stand-by periods is greatly reduced, the low pass filter system being arranged to be switched out by the operator when he prepares to receive the message signals from the calling station.

Hitherto, in radio telephone systems, it has been desirable to place the receiving antennae at a distance from the transmitting station in order to avoid interferences from the transmitter. Under such circumstances, it has been usual to provide technical operators at both the receiving and transmitting locations, or alternatively to operate the transmitters by remote control from the receiving location in order to avoid the necessity of having technical operators in constant attendance at the transmitters. Such arrangements, however, are objectionable either on account of the expense of maintaining operators at both stations, or because of the danger of damage to the transmitting equipment where no operators are present and where it is controlled remotely. Accordingly, it is preferable to have the operators at the transmitting location and the receivers operated by remote control. The present invention accomplishes this and enables the selection of a particular directional antenna from the remotely located receiver control station. These directional receiving antennae are provided to improve signalling conditions with mobile stations, such as ships at sea, when communicating with a particular ship in a certain direction.

Hitherto, when the transmitter has been switched into operation and the receiver switched out of operation, a system employing two or more relays has been provided to accomplish this switching service, one relay being operated from the voice signals received by the radio receiver, another operated by the voice signals received over the land telephone line, and a third operated by the carrier wave of the station whose messages are being received. This multiple relay system is exceedingly complicated, and liable to breakdowns, and in the present invention is replaced by a single relay operated in part by carrier signals and in part by voice currents to perform the necessary switching functions.

Hitherto also, in radio telephone stations, atmospheric static conditions have produced annoying noises in the loud speaker or head receivers while the operator has been standing by awaiting calls from distant stations. These static noises could not be avoided because of the fact that the receiver must operate at full sensitivity at such times in order to avoid missing weak signals from distant stations. The constant static noises produce severe nervous strain upon the operators, and are reduced in the present invention by the use of low pass audio filters in the loud speaker circuits during stand-by periods. The mobile stations in calling the land station, first transmit a low frequency audio tone prior to each call, this tone being passed by the filters and operating the loud speaker. The low pass filter system may thus be switched out and the receiver operated in a normal way to receive the message.

Receiver circuit The receiver circuit shown in Figures 1 and 2 consists, in general, of an antenna located portion shown in Figure l, and a remotely located portion shown in Figure 2. The receiver employs the superheterodyne principle with the equipment divided in such a manner that the radio frequency amplifiers, oscillator and first detector are located in the vicinity of the antennae, an intermediate frequency of the order of 300 to 400 kilocycles being transmitted over wired lines to the receiver control station of Figure 2, where the intermediate frequency amplifiers, second detector and audio amplifiers are located. The radio frequency amplifiers are tuned to a fixed frequency or a very narrow band of frequencies because only a single frequency or narrow band of frequencies is to be received. Unlike the ordinary superheterodyne receiver, where theintermediate frequency is fixed and the oscillator frequency is tuned to be equal to the received frequency plus or minus the intermediate frequency, the present invention employs a fixed oscillator frequency in order to avoid the necessity of tuning the oscillator by remote control. In the present invention, therefore, the intermediate frequency is not constant but varies within the narrow band of frequencies to be received. hence, the intermediate amplifier is arranged to be tuned.

Referring to the drawings in detail, Figure 1. shows the antenna located portion of the receiver circuit as designated by the numerals between Ill!) and I99. Figure 1 shows a plurality of directional antennae. two be ng shown. designated H10 and HH. These antennae are connected at the terminals Hi2 and H33 through cou ling condensers I53 and l54 to the grid circuits of the tubes I01 or I08. Inductances IM H15 and variable condensers H35. connected across the inductances I94 and IE5. perm t the tunin of the grid circuits of the tubes in? or "'8 to the particular frequency which is to be received.

The tubes H1! and IE8 are connected. respectively. to tubes I69 and Hi! in a circuit constituting a two-sta e scree grid radio freouencv amplifier for each of the antennae and NH. The grid circuits of the tubes I I!!! and Hi! are inductively coupled by means of the inductances I ,II and tuned by means of the variable condensers H2. 'JIhe usual resistors. provided inssuch 1a :radio frequency amplifying system are designated bythenumerals II3. to II.'I,inclusive,"these tbeing. duplicated for each of the=two:radio frequency amplifiers, generally designated L I I8 .and l l I 9. and associated with each directional. antenna 500 and IIlI. :Resistors I and I2I completethe amplifier circuit. By-pass condensers I22, I23, I24 and Irare likewise provided.

.The :gainof these radio-frequency amplifiers I Iiliandi I I9. is: controlled by varying' thesgrid. bias voltage from the remotely-located receiver control station, this being doneby cathode resistances conncctedacross. the cathode. by-pass conudensers. I125. The linesIZG .and 12? run for this purpose from the cathode by-pass condensers I25 to the remote receivercontrol station, and con- .nect up with theilines226 and .221 in Figure 2. The linesr226 andJ22'I (Figure'2) are connected .to a key switch'22l3,which-controls the connec- "tion of -either=ofthe variable cathode resistors $229 @1230, thereby selecting theparticular .am-

plifier II8-or .II19 and disablingthe associated amplifier. "Theadjustment of .the cathode resist- .ances229: and1230 controls the gain of the radio frequency amplifiers II8and H9 from the remotely located receiver control station.

Thus'to increase the gain of the upper twostage amplifier II8 the resistance of thevariable cathode resistor 229 between the lineiZB and the ground connection :23! is decreased. To :disable the upper amplifier r I18 the key switch .228 is operated to open the circuit between the variable cathode resistor 229 and the line 22fi,.at the same t me closing the line between thevariable cathode .resistor23ll and the line 221. By variously oper ating the keyswitchiZZfi it is thereby possible to select either :or both of .the receiving antennae ID!) or IIlI, thereby making directional or diversity reception possible. The variable cathode resister-.230 is sim larly connected to the ground at 1232. The circuit. containing the lines 226 and 227, togetherwith the key switch 228 and resistors 229and 23!), is shown and designated-by the same reference numerals in'Figure 3.

The outputs of the two radio frequency am- .plifiers Band I I9 (Figure l) are connected together at the terminal I28 and. feed into the grid tuning inductance 129 of the first detector or mixer tube I3ll. A variable condenser I3I is pro videdfor tuning'this grid tuning circuit. Resistors I32 and I33 and fixed condensers I34 and I35 are'provided in the circuits beyond the in" ductance I29. .The first detector tube IZHI also functions asan oscillator underthe control of the crystall36 having the resistor ltl bridged therearound. The oscillations of this crystal I35. in cooperation with the tuning circuit I38 having the inductance I39 and variable condenser I40, serve to convert the radio frequency signal from ltheamplifiersllll or II9 into the intermediate frequency of 300to400 kilocycles. The output of the first detector or mixer tube I38 is tuned to the intermediate frequency band by means of the :inductance& MI. and variable .condensersi I62 and The transformer I4I has the secondary winding connected tothe transmission. lines. I4 and I45, leadingto the receiver control station ("Figure 2), the same lines being there designated 2M and 2&5. The dimensions of the transformer I ii, particularly the secondary thereof, are carefully determined to procure the proper impedance xmatching .with the transmission lines I44 and M5, whichtake thesignal tothe receiver control ;associatedwiththe:circuit..of;the first detector or .mixerttube I.30;are..theresistors M6, Mland. Hi8

"mixed with the radio frequency or'signal fre- (money to produce wheat frequency between 300 'kilocycles andAOO-kilocycles, which is'taken off in the transformer ldlandtransmitted to the 'overthelineslflyud, I45.and'245. The heater "voltage for the -'various tubes (one filament only being shown for simplicity) is applied between 'tains the two-stage 'intermediate frequency am:

amplifier tubes 268 an'd 269, together with the audio transformers 2'lfi and 2'll. .The audio voltagefromrthe.seconddetector tube 20%? is fed to the potentiometer .212, the arm .of which is connected tortheagrid ofzthefirst audio tube 2%.

:station l'lShOWli 11in llligure -.2. .The .transmission lines IMzandl I45 .:may ;consist of paired lines. in

the ordinaryctelephone; cable, this. giving I good results up to zialengthvof several miles. Likewise and the fixed condensers I49, I and I5I, to ether with the jackswitch I52. In the tube I30 the crystal frequency from the crystal I36 is impe'da-ncematching transformer 20!! (Figure 2) the terminals I and'l56 and the plate voltage between the terminals I51 and I58. The jack I52 provides means'for measuring the oscillator all-r20 ode current by plugginga meter into the circuit in tuning the oscillator.

The portion of thereceiver shown inFigure 2, and termed the receiver' control station, con- .25 plifier, "generally designated'ZUI, and connected into the impedance matching transformer 2%. The two-stage amplifier ZN-contains the elec- -tronic tubes 202 and 203, the-coupling transformer 204, the output transformer 285 anclg the second detector tube 206. The portion ofthe receiver at'the receiver control station is, in

effect, 'a tuned *radio frequency receiver using tuned circuits inboth the grid and plate cir cuits. The transformers 20!], 294 and 295 have- 3 cores of powdered high frequency iron and are tuned to the intermediatefrequency corresponding to the signal to'-'-be-recei.ved by means of the ganged variable condensers 201, 208,209, 2H) and 2. Additional variablecondensers 262 to 223?.40

'and'23'I-serveto pretune the various circuits so thatthe ganged variable condensers 20! to 43H will track overtheentire scale. Additionally provided are'the fixed condensers zzi to 225 and 233 to 23$;the resistances 238 to 243 and 2th to 250.

For supplying plate voltage the rectifier cir- -cuit containing theplate "supply'rectifier tube 25I is provided together-with the transformer 252 connectedto the power lines 2'53 and 254 by a.

.50 way oftheline switch 255. The resistor and chokes =25'I and-258, together with the fixed condensers 259 to 262,- inclusive; complete the recaudio-voltage to'the-audio frequency amplifier,

generally designated 261, and having the audio The potentiometer 2l2iserves asathe audio vol-#15 ume control, and has associated therewith the fixed condenser 213. Additional resistors 214, 215 and 216, together with fixed condensers 2H, 2T3, 219 and 280 and a potentiometer 28| complete the audio amplifier circuit. The output of this two-stage audio amplifier 26'! is taken off at the lines 282 and 283.

Voice terminal circuit In Figure 3 the circuit shown in Figure 2, consisting of the receiver control station, is shown by the same reference numerals. The entire amplifying and detecting system, however, and including the radio frequency amplifier 2Ul, audio frequency amplifier 261 and rectifier circuit, is indicated diagrammatically and designated the receiver 284. This numeral 284 refers to all of the equipment shown in Figure 2 excepting the circuit 226 to 232, controlled by the key switch 228 for selecting and controlling the receiver circuit shown in Figure l. The latter may be mounted upon or near the masts of the antennae and requires no constant attendance of an operator.

The output of the receiver 284 from the lines 282 and 283 (Figure 3) is connected through the normally closed contacts of the key switch 338 to the low pass filter circuit, generally designated 30L and consisting of the transformers 302 and 333, the inductances 304 and 335 and the fixed condensers 336, 301 and 338 and an amplifier 333, which in turn, is connected to a loud speaker 3! I]. The key switch 3 is provided for cutting the low pass filter circuit 3M out of the circuit of the loud speaker 3M.

The low pass filter circuit 3M eliminates most of the static noise, but passes the low frequency tone transmitted from the ship prior to each call. When the operator hears this tone from the loud speaker 3 l 9 he may operate the key switch 33 I to cut the filter circuit 3E5| out of the circuit of the loud speaker M0, or else he may operate the key 303 to disconnect the filter circuit 3M and loud speaker 3"], together with its amplifier 3M, and simultaneously to connect the output lines 282 and 283 of the receiver 284 to the telephone head phones 3I2.

Beyond the key switch 300 the receiver output lines 282 and 283 are connected into the primary of a transformer 3l3, the secondary of which is connected to the lines 3! and 3|5, respectively. The line 3l4 runs to the key switch 3l5 by which the relay 3!? may be cut into or out of operation. The relay 3H is provided with a relay-operating coil 3l8, connected at the terminal 3H3 to a suitable source of positive current, and on its other side connected to the line 320 leading to the terminal 32 I. The line 3l5 from the transformer 3 l 3 is connected beyond the relay 3|! to the repeat coil or transformer 322 by way of the line 323. From the opposite terminal of this winding of the repeat coil 322 the line 324 runs to the op posite terminal of the relay 3H. The other winding of the repeat coil 322 is connected to the land or wired telephone lines 325 and 326, leading to the land telephone system with which it may be desired to connect the radio telephone system for direct communication between a ship station and a land telephone subscriber.

Beyond the key switch 3H3 and relay 3H the lines 321 and 328 run to one winding of the transformer 329, the opposite winding of which is connected by the lines 333 and 33! to the transmitting amplifier 332. The output lines 333 and 334 of the latter run to the attenuation device 335, from which the lines 336 and 33'! run to the radio transmitter 338. The details of the radio transmitting system are immaterial to the present invention. The lines 336 and 33'! are connected by the lines 339 and 340 to one winding of a transformer 34l, the other winding of which is connected into the plate and grid circuit of a vacuum tube 342, forming a part of the switching circuit, generally designated 343. Besides the tube 342 the switching circuit 343 contains electronic tubes 344 and 345, having their plates connected through the milliammeters 346 and 347 to the terminal 32| of the line 32!] leading to the operating coil 3? of the relay 3H. In this manner plate current from either of the tubes 344 or 345 will energize the relay coil 3l8 and operate the relay 3H.

The tube 343 is hereinafter called the voice tube and is normally biased to cut oil i. e. zero plate current by means of the potentiometer 348 in its cathode circuit. The tube 344, on the other hand, hereinafter called the carrier tube, is normally biased by means of the potentiometer 333 in its screen grid circuit so as to pull a predetermined amount of current, for example, two.

milliamperes. This current holds the relay 3H in an operated condition (Figure 3), shunting out the radio receiver output circuit and leaving the land telephone lines 323 and 324 connected to the radio transmitter input lines 336" and 33?. The switching circuit 343 is completed by the fixed condenser 35D and the resistors 35l to 354, inclusive. Between the resistors 353 and 354, the terminal 355 is connected to the line 356 leading to a source of positive 13 voltage, such as 300 volts, this connection being similar to that of the terminal 3|9 of the relayoperating coil 3l8, and completing the relayoperating coil circuit.

The control grid of the carrier tube 344 is connected to the automatic volume control voltage of the radio receiver 284 through the line 26 5, previously mentioned. The tubes in the receiver which have this automatic volume control voltage applied to their grids are of the variablemu. type and require a high bias voltage for plate current cut-off. The tube 344, which may be of the type known commercially as the type 606, is an abrupt cut-oil tube. Accordingly, when a normal signal is received from the radio receiver 284 enough bias voltage will be generated to completely block the carrier tube 344. Since the carrier tube plate current normally holds the relay 3ll operated to connect the land telephone lines and 324 with the radio transmitter 338, every time a signal is received by the radio receiver 284 the voice-controlled carrier will set up enough bias voltage to block the carrier tube 344, which in turn, allows the relay 3i! to move against its back or upper contact. The carrier is transmitted by the remote station only when talking, the transmitter being put into operation by voice signals.

When the relay drops the output of the receiver 284 is automatically connected directly to the land telephone lines 323 and 324, and the radio transmitter input is automatically shunted out. When the radio telephone party at the distant station stops talking, the carrier disappears, the automatic volume control voltage over the line 253 drops, and the carrier tube 344 draws current. This current energizes the relay coil 3l8 to operate the relay 3H, and the land telephone party is again connected to the radio transmitter 333. When the land telephone party begins to talk a small portion of the audio input to the radio transmitter 338 is fed through the lines 339 and 343 to the transformer 34!, thence to the tube 342, which rectifies this voltage and places the rectified voltage on the grid of the voice tube 345.

This rectified voltage from the tube 342 operates to make the grid of the voice tube 345 less negative, or in the case of strong signals, actually positive with respect to the cathode of the voice tube 345. This change in the grid voltage on the grid of the voice tube 345 causes plate current to flow from the plate thereof, which supplements the current through the relay coil 3l8 from the carrier tube 344, thereby causing the armature 3 l 1 to maintain its contact with the front or lower contact member, even though static crashes might occur while the land telephone party is talking. The attenuator 335 serves for adjusting the speech volume fed into the radio transmitter.

Operation Much of the operation of the radio system of this invention has been described in connection with the respective circuits. When the operator at the receiver control "station, in Figure 2, desires to communicate with a particular ship in a known direction, he selects either or both of the directional receiving antennae H'lfl or ID! by manipulating the key switch 228, in the manner previously described. This automatically connects the radio frequency amplifier H8 or i l3 with the cathode variable resistors 229 or 236, by which the gain of each amplifier may be adjusted from the receiver control station.

When a ship calls, it first sends out a low audio tone, which is received over one of the -antennae ill!) or 19 l, amplified through the selected radio frequency amplifier H8 or I 13, and mixed in the first detector tube 139 with the crystal frequency from the crystal I36 to produce a beat frequency between 300 and 400 kilocycles. This passes through the impedance matching transformer l4! and over the lines 144, 145, 244 and 245, through the impedance matching transformer 206 to the intermediate frequency amplifier 2M, which has been adjusted by means of the ganged condensers 201 to 21! to receive the ships frequency. The signal continues through the audio frequency amplifier 261 and over the output'lin'es 282 and. 283, through the key switch 300 and low pass filter system 3M to the amplifier 309 and loud speaker am, where it sounds the low tone. This warns the operator of the presence of the signal and he then manipulates the key 3 to cut out the low pass filter circuit 3M from the loud speaker 3) so as to hear the message signals directly over the loud speaker 3H1, or else he manipulates the key switch 300 to transfer the message signals to his-head phones 31 2. The ship then transmits the message signals upon the selected frequency, and these message signals operate the switching system 343, in the manner previously described, to actuate the relay 3H in such a manner as to connect the land telephone lines 325 and 326 to the radio receiver 284 (Figure 3). The relay 3 l 8, however, may be placed in or out of operation by manipulating the key switch 3| 6. The land party then listens to the message.

ing the land telephone party to the radio transmitter 338. When the land telephone party begins to' talk the audio input current, which passes through the transformer 3 to the tube 342 of the switching circuit 343, causes plate current to flow in the voice-operated tube 345, which supplements the current through the relay coil 3! from the carrier tube 344, thereby holding the relay 3|! against its front or lower contact, irrespective of the fact that static crashes may occur while the land party is talking. When the land party ceases talking and a radio signal is again received by the radio receiver 284, the switching system 343 and relay 311 again operate to connect the radio receiver 284 to the land telephone lines 325 and 326, in the manner previously described.

Thus, the carrier tube normally holds the relay 3l'l in position to connect the radio transmitter 338 tothe land telephone lines 325 or 325. The voice currents produced in the land lines 325 and 326 are rectified by the tube 342, and applied to the voice tube 345 in such a manner as to hold the relay 3H in the transmitting position so long as the voice currents from the land telephone party continue to arrive over the lines 325 and 326.

When a carrier wave arrives in the radio" receiver 284, however, a negative voltage is generated thereby, which is conveyed to the carrier tube 344 in such a manner as to cut off its plate current and the relay 311 is released to make contact with its upper terminal. When neither the carrier tube 344 nor the voice tube 345 pulls current through the relay coil 318, the radio signal received may pass through the relay 3H to the land lines 325 and 326.

The term diversity reception is used herein as commonly used to denote receiving the same radio signal on several antennae as high frequency waves do not fade at the same efficiency on antennae relatively close to each other. The variable condenser 231 permits the adjustment of the radio frequency detector circuit to a condition where gauging it with the amplifier grid and plate tuning condensers is made possible. On diode detectors the load is quite different from the load on the amplifier grid and plate circuits, and hitherto this has made it quite difficult to gang the diode tuning condenser with the amplifier grid and plate tuning condensers. In place of the relay 3" switching by means of tubes, copper oxide rectifiers or other analogous devices might alternatively be employed. It will also be understood that the signal announcing means responsive to low audio frequency signals only may include loud speakers mechanically tuned to respond to low frequencies only, or mechanical low pass filters and other devices, excluding high audible frequencies and passing only low audible frequencies.

It will be understood that I desire to compre- I hend within my invention such modifications as come within the scope of the claims and the invention.

Having thus fully described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. In a radio station, a radio receiver, a radio transmitter, a wired telephone circuit, switching means for selectively connecting said wired telephone circuit to said radio receiver and transmitter respectively, means responsive solely to carrier signals for operating said switching means to connect said wired telephone circuit with said radio receiver, and voice-responsive means for operating said switching means to connect said wired telephone circuit with said radio transmitter.

2. In a radio station, a radio receiver, a radio transmitter, a wired telephone circuit, switching means for selectively connecting said wired telephone circuit to said radio receiver and transmitter respectively, an electronic tube circuit responsive solely to carrier signals for operating said switching means to connect said wired telephone circuit with said radio receiver, and a voice-responsive electronic tube circuit for operating said switching means to connect said wired telephone circuit with said radio transmitter.

3. In a radio station, a radio receiver, a radio transmitter, a wired telephone circuit, a relay for selectively connecting said wired telephone circuit to said radio receiver and transmitter respectively, carrier-signal-responsive means for operating said relay to connect said wired telephone circuit with said radio receiver, and voiceresponsive means for operating said relay to con nect said wired telephone circuit with said radio transmitter.

4. In a radio station, a radio receiver, a radio transmitter, a wired telephone circuit, a relay constituted of a single actuating coil and armature for selectively connecting said wired telephone circuit to said radio receiver and transmitter respectively, a carrier-signal-responsive electronic tube circuit for operating said relay to connect said wired telephone circuit with said radio receiver, and a voice-responsive electronic tube circuit for operating said relay to connect said wired telephone circuit with said radio transmitter.

5. In a radio station, a radio receiver, a radio transmitter, a wired telephone circuit, a relay for selectively connecting said wired telephone circuit to said radio receiver and transmitter respectively, means including a radio-signal-responsive electronic tube having abrupt cut-off characteristics for operating said relay to connect said wired telephone circuit with said radio receiver, and a voice-responsive electronic tube circuit for operating said relay to connect said wired telephone circuit with said radio transmitter.

6. In a radio station, a radio receiver, a radio transmitter, a wired telephone circuit, a relay for selectively connecting said wired telephone circuit to said radio receiver and transmitter respectively, a radio-signal-responsive electronic tube circuit for operating said relay to connect said wired telephone circuit with said radio receiver, and means including a voice-responsive electronic tube biased to draw a predetermined current for operating said relay to connect said wired telephone circuit with said radio transmitter.

7. In a radio station, a radio receiver, a radio transmitter, a wired telephone circuit, a relay for selectively connecting said wired telephone circuit to said radio receiver and transmitter respectively,

a radio-signal-responsive electronic tube circuit for operating said relay to connect said wired telephone circuit with said radio receiver, and a voice-responsive electronic tube circuit for operating said relay to connect said wired telephone circuit with said radio transmitter, said voice-responsive electronic tube circuit including an electronic tube biased to draw a predetermined current and a rectifier tube adapted to rectify voice currents and supply the rectified voltage to said voice-responsive tube to cause plate current to flow therefrom through said relay, whereby to maintain the position of said relay irrespective of the currents of static crashes during the transmission of voice signals from said wired telephone circuit to said transmitter.

8. In combination, a radio receiver, a radio transmitter, a wired telephone circuit, a relay for selectively connecting said wired telephone circuit to said radio receiver and transmitter respectively, means for maintaining the operating coil of said relay in an energized condition whereby the wired telephone circuit is normally connected to said radio transmitter, and means responsive to currents of carrier frequency for disabling said maintaining means whereby the operating coil of said relay is deenergized to make a connection between the wired telephone circuit and the radio receiver.

9. In combination, a radio receiver, a radio transmitter, a wired telephone circuit, a relay for selectively connecting said wired telephone circuit to said radio receiver and transmitter respectively, means for maintaining the operating coil of said relay in an energized condition whereby the wired telephone circuit is normally connected to said radio transmitter, means including a voice-operated device for supplementing the current through said maintaining means, and means responsive to currents of carrier frequency for disabling said maintaining means whereby the operating coil of said relay is deenergized to make a connection between the wired telephone circuit and the radio receiver.

10. In combination, a radio receiver, a radio transmitter, a wired telephone circuit, a relay for selectively connecting said wired telephone circuit to said radio transmitter respectively, means for maintaining the operating coil of said relay in an energized condition whereby the wired telephone circuit-is normally connected to said transmitter, and means responsive to currents in a carrier frequency circuit for disabling said maintaining means whereby the operating coil of said relay is deenergized to make a connection between the wired telephone circuit and the radio receiver, and means for preventing a false operation of said disabling means brought about by static crashes in the carrier frequency circuit, said falseoperation-preventing means comprising a voiceoperated relay which serves to supplement the current in said maintaining means during the time the wired telephone circuit is connected to the radio transmitter.

DONALD A. HEISNER. 

